For example, a heat exchanger has a plurality of tubes through which an internal fluid flows, a first tank for distributing the internal fluid into the tubes and a second tank for collecting the internal fluid from the tubes. The inlet tank has an inlet port on its first end and the outlet tank has an outlet port on its first end. The inlet port and the outlet port are disposed on the same side with respect to a tube stacking direction in which the tubes are stacked. Such a heat exchanger is used, for example, as a heating heat exchanger (heater core) for a vehicular air conditioning apparatus.
In the inlet tank of the heat exchanger, pressure loss of the internal fluid (e.g. heated fluid) increases with a distance from the inlet port due to the length of the inlet tank. Therefore, the volumes of the internal fluid flowing into some tubes that are located farther away from the inlet port are smaller than the volumes of the internal fluid flowing into some tubes that are located closer to the inlet port. That is, the volumes of the internal fluid are likely to be uneven between the tubes. With this, distribution of air temperature downstream of the heat exchanger with respect to a flow of air is uneven, resulting in deterioration of air conditioning feeling.
For example, Unexamined Japanese Patent Publication No. 9-14885 discloses a heater core that has a structure for reducing difference of the pressure loss of the internal fluid, such as internal fluid, throughout the inlet tank, thereby to make the volume of the internal fluid substantially uniform between the tubes. In the disclosed heater core, two separation plates are arranged in the inlet tank so that three passages having different length are formed inside of the inlet tank.
The tubes are divided into three groups from the inlet port in the tube stacking direction, and the tubes of each group correspond to each passage. Thus, the internal fluid is substantially uniformly distributed into the tubes from the corresponding passages.
Specifically, a first separation plate and a second separation plate extend in the tube stacking direction, but are spaced from each other in a tube longitudinal direction. The first separation plate is arranged closer to ends of the tubes, and the second separation plate is arranged farther away than the first separation plate with respect to the ends of the tubes. The first separation plate is shorter than the second separation plate, and extends to overlap the tubes of a first group, which is closer to the inlet port, with respect to the tube stacking direction. The second separation plate extends to overlap the tubes of the first group and the tubes of a second group, which is between the first group and a third group, with respect to the tube stacking direction.
Namely, a first passage is defined between the ends of the tubes of the first group and the first separation plate. A second passage is defined between the first separation plate and the second separation plate. A third passage is defined between the second separation plate and a wall of the inlet tank. The first passage is the shortest and the third passage is the longest.
The internal fluid flowing through the first passage is introduced into the tubes of the first group. The internal fluid flowing through the second passage is introduced into the tubes of the second group. The internal fluid flowing through the third passage is introduced into the tubes of the third group.
If the first to third passages have the same flow area (cross-sectional area), the pressure loss of the internal fluid flowing into the tubes of the first group is smaller, and the pressure loss of the internal fluid flowing into the tubes of the third group is larger, due to the differences of the length. In the inlet tank of the disclosed heater core, therefore, the three passages have different cross-sectional areas such that the first passage has the smallest cross-sectional area and the third passage has the largest cross-sectional area.
As such, because the flow speed of the internal fluid in the first passage relatively increases, the pressure loss of the internal fluid flowing into the tubes of the first group increases. Because the flow speed of the internal fluid in the third passage relatively reduces, the pressure loss of the internal fluid flowing into the tubes of the third group reduces.
By this structure, since the pressure loss of the internal fluid flowing into the tubes of the three groups is substantially uniform, the volume of the internal fluid is substantially uniform between the tubes of the three groups. On the other hand, it is necessary to accurately position the separation plates to maintain the respective cross-sectional areas of the three passages. Further, the volumes of the internal fluid in the tubes will be more uniform by increasing the number of the separation plates. However, the structure of the inlet tank becomes complex.